docs(chatkit): document Telnyx relay and OpenAI voice setup

[danielblignaut]

Change

Document Telnyx Conversation Relay and OpenAI voice modes with agent-owned speech settings, normal ChatKit sessions, typed callback context, interruption provenance, and manual browser/phone testing. Include exact REST/configuration fields and the distinction between self-managed and managed webhook setup for an existing customer application.

Validation

mint validate, mint broken-links, mint a11y, and npm run check:publication-boundary pass. The guide does not claim a real Telnyx call, browser microphone test, or deployment. Current main's custom-provider and direct-resource guides are integrated.

Documentation and publication

Affected public pages: chatkit.mdx and llms/chatkit.md; voice adds no navigation entry. Detailed architecture/change records remain in the owning source repositories, following the current public-docs publication policy.

• API and ADR 0027: https://github.com/trytilde/api/pull/277
• SDK and manual example: feat(sdk): add Telnyx relay voice context and examples dispatch#155
• Release order: API/migrations, SDK package release, then this guide.

Managed webhook setup does not buy/assign numbers or provision a Tilde-funded carrier account. Direct WebRTC/SIP, ElevenLabs, recordings, voice-note conversion, native endpoint-tool bridging, and browser personal-tool federation remain outside this release.